storage

Some of you might have noticed that UniShare has its own folder in your devices picture library. Also some other apps like WhatsApp or Tweetium have it. The advantages of your app’s own folder are clear:

• easier to get images into your app
• user can always reflect which pictures come from your app
• another presence of your app within the OS
• higher remember rate for your app at the user site (which leads to more frequent usage of your app)

This post will show you how easy it is to generate a folder into the Pictures Library as well as save and read files into/from this folder.

Preparation

First, you need to add this using statements to your app:

using Windows.Storage;
using Windows.Storage.Streams;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Media.Imaging;

Next, add the Picture Library capabilities to your app’s Package.appmanifest.

If you have a 8.1 Silverlight app, you need to add it to both the Package.appmanifest as well as the WMAppManifest.xml:

Then we are already able to generate our folder with this single line of code (counts for both Silverlight and Runtime apps):

StorageFolder appFolder= await KnownFolders.PicturesLibrary.CreateFolderAsync("myCustomAppFolder", CreationCollisionOption.OpenIfExists);

You should always use the CreateFolderAsync method together with the CollisionOption ‘OpenIfExists’. This way, your app will open it every time you are going to save a file, but creates the folder if it does not exist yet. If you now go to your pictures library, you will not see your folder yet, although it is there (use a File Manager app to check it if you want). Folders do only get populated when they have content. This is what the next step is about.

Save an image file

Saving an image is also pretty straight forward. First we are generating a StorageFile within our folder:

StorageFile myfile= await appFolder.CreateFileAsync("myfile.jpg", CreationCollisionOption.ReplaceExisting);

This generates a File Container that we can write our image to. To save the image we are going to asynchronously write the Stream of our image into it:

//asuming we have an Image control, replace this with your local code
var img = myImage.Source as WriteableBitmap;
//get fresh drawn image 
img.Invalidate();

using (Stream stream = await myfile.OpenStreamForWriteAsync())
{
   img.SaveJpeg(stream, img.PixelWidth, img.PixelHeight, 0, 100);
}

This code works for both a Windows Phone 8.1 Silverlight and Runtime apps. If you now go to your Pictures library, you will see your app’s folder as well as your saved image. Pretty easy, right?

Read images from our app’s folder

Reading an image file is pretty easy as well. Here is the code:

//open the picture library
StorageFolder libfolder = KnownFolders.PicturesLibrary;
//get all folders first
IReadOnlyList<StorageFolder> folderList = await libfolder.GetFoldersAsync();
//select our app's folder
var appfolder = folderList.FirstOrDefault(f => f.Name.Contains("myCustomAppFolder"));
//get the desired file (assuming you know the file name)
StorageFile picfile = await appPicturesFolder.GetFileAsync("myfile.jpg");
//generate a stream from the StorageFile
var stream = await picfile.OpenAsync(FileAccessMode.Read);
//generate a new image and set the source to our stream
BitmapImage img = new BitmapImage();
img.SetSource(stream);

//todo: work with the image

To get our generated folder, we need to fetch a list of folders in the library using the StorageFolder.GetFoldersAsync() method. We then query this list for our app’s folder. If you want to get a list of all pictures in your folder, you can use the StorageFile.GetFilesAsync() method. What I have done above is to load our saved single file. Finally, I opened a stream from this file and assigned it to a new BitmapImage, which can be used in our app.

There are also a lot of other options one can do with these folders and files, this is a very common scenario.

As always, I hope this post is helpful for some of you.